Abstract

We consider the absorption by bound electrons of dark matter in the form of dark photons and axion-like particles, as well as of dark photons from the Sun, in current and next-generation direct detection experiments. Experiments sensitive to electron recoils can detect such particles with masses between a few eV to more than 10 keV. For dark photon dark matter, we update a previous bound based on XENON10 data and derive new bounds based on data from XENON100 and CDMSlite. We find these experiments to disfavor previously allowed parameter space. Moreover, we derive sensitivity projections for SuperCDMS at SNOLAB for silicon and germanium targets, as well as for various possible experiments with scintillating targets (cesium iodide, sodium iodide, and gallium arsenide). The projected sensitivity can probe large new regions of parameter space. For axion-like particles, the same current direction detection data improves on previously known direct-detection constraints but does not bound new parameter space beyond known stellar cooling bounds. However, projected sensitivities of the upcoming SuperCDMS SNOLAB using germanium can go beyond these and even probe parameter space consistent with possible hints from the white dwarf luminosity function. We find similar results for dark photons from the sun. For allmore » cases, direct-detection experiments can have unprecedented sensitivity to dark-sector particles.« less

@article{osti_1426146,
title = {Searching for dark absorption with direct detection experiments},
author = {Bloch, Itay M. and Essig, Rouven and Tobioka, Kohsaku and Volansky, Tomer and Yu, Tien-Tien},
abstractNote = {We consider the absorption by bound electrons of dark matter in the form of dark photons and axion-like particles, as well as of dark photons from the Sun, in current and next-generation direct detection experiments. Experiments sensitive to electron recoils can detect such particles with masses between a few eV to more than 10 keV. For dark photon dark matter, we update a previous bound based on XENON10 data and derive new bounds based on data from XENON100 and CDMSlite. We find these experiments to disfavor previously allowed parameter space. Moreover, we derive sensitivity projections for SuperCDMS at SNOLAB for silicon and germanium targets, as well as for various possible experiments with scintillating targets (cesium iodide, sodium iodide, and gallium arsenide). The projected sensitivity can probe large new regions of parameter space. For axion-like particles, the same current direction detection data improves on previously known direct-detection constraints but does not bound new parameter space beyond known stellar cooling bounds. However, projected sensitivities of the upcoming SuperCDMS SNOLAB using germanium can go beyond these and even probe parameter space consistent with possible hints from the white dwarf luminosity function. We find similar results for dark photons from the sun. For all cases, direct-detection experiments can have unprecedented sensitivity to dark-sector particles.},
doi = {10.1007/JHEP06(2017)087},
journal = {Journal of High Energy Physics (Online)},
number = 6,
volume = 2017,
place = {United States},
year = {2017},
month = {6}
}

An ever-increasing amount of evidence suggests that approximately one quarter of the energy in the universe is composed of some non-luminous, and hitherto unknown, “dark matter”. Physicists from numerous sub-fields have been working on and trying to solve the dark matter problem for decades. The common solution is the existence of some new type of elementary particle with particular focus on weakly interacting massive particles (WIMPs). One avenue of dark matter research is to create an extremely sensitive particle detector with the goal of directly observing the interaction of WIMPs with standard matter. The Cryogenic Dark Matter Search (CDMS) projectmore » operated at the Soudan Underground Laboratory from 2003–2015, under the CDMS II and SuperCDMS Soudan experiments, with this goal of directly detecting dark matter. The next installation, SuperCDMS SNOLAB, is planned for near-future operation. The reason the dark-matter particle has not yet been observed in traditional particle physics experiments is that it must have very small cross sections, thus making such interactions extremely rare. In order to identify these rare events in the presence of a background of known particles and interactions, direct detection experiments employ various types and amounts of shielding to prevent known backgrounds from reaching the instrumented detector(s). CDMS utilized various gamma and neutron shielding to such an effect that the shielding, and other experimental components, themselves were sources of background. These radiogenic backgrounds must be understood to have confidence in any WIMP-search result. For this dissertation, radiogenic background studies and estimates were performed for various analyses covering CDMS II, SuperCDMS Soudan, and SuperCDMS SNOLAB. Lower-mass dark matter t c2 inent in the past few years. The CDMS detectors can be operated in an alternative, higher-biased, mode v to decrease their energy thresholds and correspondingly increase their sensitivity to low-mass WIMPs. This is the CDMS low ionization threshold experiment (CDMSlite), which has pushed the frontier at lower WIMP masses. This dissertation describes the second run of CDMSlite at Soudan: its hardware, operations, analysis, and results. The results include new WIMP mass-cross section upper limits on the spin-independent and spin-dependent WIMP-nucleon interactions. Thanks to the lower background and threshold in this run compared to the first CDMSlite run, these limits are the most sensitive in the world below WIMP masses of ~4 GeV/c 2. This demonstrates also the great promise and utility of the high-voltage operating mode in the SuperCDMS SNOLAB experiment.« less

Observations of galaxies, superclusters, distant supernovae, and the cosmic microwave background radiation indicate that 85% of the matter in the universe is nonbaryionic. Understanding the nature of this so-called dark matter is of fundamental importance to cosmology, astrophysics, and high energy particle physics and is specifically highlighted in the SNOWMASS 2013 High Energy Physics community report. Although Weakly Interacting Massive Particles (WIMPs) of mass 10-100 GeV/c2 have been the main interest of the majority of direct dark matter detection experiments, recent signal claims, together with compelling new theoretical models, are shifting the old paradigm towards broader regions in the darkmore » matter parameter space well below 10 Gev. The SuperCDMS SNOLAB experiment is seeking to directly detect dark matter using very sensitive, low threshold germanium or silicon semiconductor detectors operating at millikelvin temperatures. An improved version of this detector technology makes an entirely new frontier accessible that hitherto has only been in the planning stages at various facilities. Nearly thirty years ago, Freedman determined that the neutrino-nucleon neutral current interaction leads to a coherence effect, whereby the elastic scattering cross section is enhanced and scales approximately as the square of the number of neutrons in the nucleus. Hence, for typical nuclear radii, coherent scattering leads to nuclear recoils in the range of a few keV for incoming neutrinos with energies in the range ~ 1-100 MeV. Although CEνNS is a fundamental prediction of the Standard Model, it has not been measured until recently and may open a window to new physics. The expected CEνNS cross-section is many orders of magnitude higher than the coherent WIMP nucleon scattering cross-section excluded by current generation experiments for standard heavy WIMPs. However, this process has a low recoil energy endpoint ( We expect interactions from both light mass WIMPs and CEνNS to produce nuclear recoils of a few tens of eV, as measured by the nuclear recoil channel. Thus, both experiments strive to develop very low threshold detectors, preferably with single electron-hole pair resolution. Due to the Ge/Si crystallographic orientation dependence of e-h excitations at such extremely low thresholds, these data can help steer the design of future (G2+ and G3) detectors wherein the solar neutrino scattering becomes a major background for DM experiments. Since September 2016, Mirabolfathi has initiated a collaborative effort with the K. Nordlund computational physics and matter-radiation interaction group at the University of Helsinki to study energy threshold for e-h excitations from nuclear recoils in Ge or Si crystals. Our computational results show that those thresholds are well below the Lindhard estimate and exhibit strong crystallographic orientation dependence. This could pave the way for directional sensitivity to the WIMP-detector interaction and ultimately provide a gateway for a directional DM search with condensed matter detectors, i.e. the holy grail in the DM direct search community. On the other hand, observational astronomy has long implemented Charge Coupled Devices (CCD), and recently dark matter searches have started to do the same. The excellent ionization resolution offered by CCDs makes them one of the most suitable technologies for very low mass dark matter searches. However, they are difficult to scale up in mass because the detectors need to be depleted to suppress thermally generated carriers in semiconductors. Even made from the purest Si substrates available, detectors thicker than 1 mm are difficult to deplete. Recently, single electron detection has been demonstrated with skipper CCD’s with unprecedented < 1 electron resolution. DAMIC (Dark Matter) and CONNIE (CEνNS) are experiments that use CCD technology for event searches but, because of depletion limitations, suffer from a small payload mass. The only way for these experiments to increase mass is by making more modules, which increases the readout electronics necessary and hence the cost. We propose a method to increase CCD mass per module by freezing the minority carriers rather than depleting them. Among the most suitable devices to search for low-mass WIMPs are the SuperCDMS experiment phonon-mediated detectors. They offer very low threshold to detect low mass WIMPs as well as high resolution due to phonon mediated sub-kelvin detector technology. SuperCDMS uses two detector types specifically designed for different WIMP mass ranges: 1) The iZIP technology, which uses simultaneous measurement of ionization and phonons to discriminate Nuclear Recoil (NR) expected WIMP interaction events from Electron Recoil (ER) radioactive background events, and 2) SuperCDMS HV technology, which is based on indirect, but very sensitive, measurement of ionization via Neganov-Luke (NL) phonon amplification. In the absence of leakage current, the detector sensitivity improves proportionally to the applied bias across the detector and can in principle reach the ultimate quantum limit of single electron hole pair threshold of ~eV. Our current SuperCDMS HV detector technology is underperforming at large voltages due to an early onset of leakage current that deteriorates our signal-to-noise gain. We are proposing a method to solve both the scalability of CCD technology and HV leakage in NL amplification assisted CDMS detectors. The idea combines both technologies to make sub- kelvin phonon-assisted CCD readout. CDMS already proved that at sub-kelvin temperatures, carriers drift over large distances for fields as low as ~V/cm without significant ionization loss. This matches our expectation from semiconductor physics since all carriers and impurities are frozen at these low temperatures, making depletion superfluous. CCD electrode architecture also alleviates the ionization leakage drawback in CDMS HV technology since, assuming a long enough carrier lifetime and a low amplitude alternating bias, one can achieve similar phonon gain compared to HV DC bias.« less

Dark matter in the sub-GeV mass range is a theoretically motivated but largely unexplored paradigm. Such light masses are out of reach for conventional nuclear recoil direct detection experiments, but may be detected through the small ionization signals caused by dark matter-electron scattering. Semiconductors are well-studied and are particularly promising target materials because their O(1 eV) band gaps allow for ionization signals from dark matter particles as light as a few hundred keV. Current direct detection technologies are being adapted for dark matter-electron scattering. In this paper, we provide the theoretical calculations for dark matter-electron scattering rate in semiconductors, overcomingmore » several complications that stem from the many-body nature of the problem. We use density functional theory to numerically calculate the rates for dark matter-electron scattering in silicon and germanium, and estimate the sensitivity for upcoming experiments such as DAMIC and SuperCDMS. We find that the reach for these upcoming experiments has the potential to be orders of magnitude beyond current direct detection constraints and that sub-GeV dark matter has a sizable modulation signal. We also give the first direct detection limits on sub-GeV dark matter from its scattering off electrons in a semiconductor target (silicon) based on published results from DAMIC. We make available publicly our code, QEdark, with which we calculate our results. Our results can be used by experimental collaborations to calculate their own sensitivities based on their specific setup. In conclusion, the searches we propose will probe vast new regions of unexplored dark matter model and parameter space.« less

A substantial amount of astrophysical evidence indicates that approximately a quarter of all energy in the universe is composed of a nonluminous, and nonbaryonic \dark" matter. Of the potential dark matter particle candidates, Weakly Interacting Massive Particles, or WIMPs, is particularly well motivated. As a means to directly detect WIMP interactions with baryonic matter, the Cryogenic Dark Matter Search (CDMS) project was established, operating at the Soudan Underground Laboratory from 2003 - 2015, under the CDMS II and SuperCDMS Soudan experiments. CDMS detectors simultaneously measure the ionization and phonon energies of recoil events in Si and Ge crystals kept atmore » cryogenic temperatures in a low-background environment. The ratio of ionization energy to recoil energy serves as a discrimination parameter to separate nuclear recoil events from the electron-recoil background. The next installation, SuperCDMS SNOLAB, is preparing for future operation, with an initial payload of eighteen Ge and six Si, 100 mm diameter, 33 mm thick detectors. Of this initial payload, eight Ge and four Si detectors will operate in a high-voltage ( 100 V) mode, which have an increased sensitivity to low-mass WIMPs due to decreased energy thresholds. The SuperCDMS test facility at University of Minnesota aids in the detector R&D and characterization of prototype detectors, as part of the scale-up eort for Super- CDMS SNOLAB. This thesis presents the rst full ionization and phonon characterization study of a 100 mm diameter, 33 mm thick prototype Ge detector with interleaved phonon and ionization channels. Measurements include ionization collection eciency, surface event rejection capabilities, and successful demonstration of nuclear recoil event discrimination. Results indicate that 100 mm diameter, interleaved Ge detectors show potential for use in SuperCDMS SNOLAB. As part of detector R&D, the Minnesota test facility also looks beyond the next stage of SuperCDMS, investigating larger individual detectors as a means to easily scale up the sensitive mass of future searches. This thesis presents the design and initial testing results of a prototype 150 mm diameter, 33 mm thick silicon ionization detector, which is 5.2 times larger than those used in SuperCDMS at Soudan and 2.25 times larger than those planned for use at SuperCDMS SNOLAB. In addition, the detector was operated with contact-free ionization electrodes to minimize bias leakage currents, which can limit operation at high bias voltages. The results show promise for the operation of both large volume silicon detectors and contact-free ionization electrodes for scaling up detector mass and bias.« less

Over 80 years ago we discovered the presence of Dark Matter in our universe. Endeavors in astronomy and cosmology are in consensus with ever improving precision that Dark Matter constitutes an essential 27% of our universe. The Standard Model of Particle Physics does not provide any answers to the Dark Matter problem. It is imperative that we understand Dark Matter and discover its fundamental nature. This is because, alongside other important factors, Dark Matter is responsible for formation of structure in our universe. The very construct in which we sit is defined by its abundance. The Milky Way galaxy, hencemore » life, wouldn't have formed if small over densities of Dark Matter had not caused sufficient accretion of stellar material. Marvelous experiments have been designed based on basic notions to directly and in-directly study Dark Matter, and the Cryogenic Dark Matter Search (CDMS) experiment has been a pioneer and forerunner in the direct detection field. Generations of the CDMS experiment were designed with advanced scientific upgrades to detect Dark Matter particles of mass O(100) GeV/c 2. This mass-scale was set primarily by predictions from Super Symmetry. Around 2013 the canonical SUSY predictions were losing some ground and several observations (rather hints of signals) from various experiments indicated to the possibility of lighter Dark Matter of mass O(10) GeV/c 2. While the SuperCDMS experiment was probing the regular parameter space, the CDMSlite experiment was conceived to dedicatedly search for light Dark Matter using a novel technology. "CDMSlite" stands for CDMS - low ionization threshold experiment. Here we utilize a unique electron phonon coupling mechanism to measure ionization generated by scattering of light particles. Typically signals from such low energy recoils would be washed under instrumental noise. In CDMSlite via generation of Luke-Neganov phonons we can detect the small ionization energies, amplified in phonon modes during charge transport. This technology allows us to reach very low thresholds and reliably measure and investigate low energy recoils from light Dark Matter particles. This thesis describes the physics behind CDMSlite, the experimental design and the first science results from CDMSlite operated at the Soudan Underground Laboratory.« less